As the digital still camera becoming popular recently, the digital video camera originally designed for moving picture is also used in recording of still picture, and in such case the digital video camera is required to record a still picture at a picture quality as high as in the case of the digital still camera exclusive for still picture. However, the DV standard for moving picture specifies the number of output pixels of digital video camera. For example, the DV standard specifies the number of output pixels of the NTSC system as horizontal 720 pixels×vertical 480 pixels. Therefore, the conventional digital video camera, in the case of output of still picture, must generate in this number of pixels (720 pixels×480 pixels). As a result, the picture quality of still picture by the digital video camera is limited at a level equivalent to the VGA (640 pixels×480 pixels).
More recently, using a charge coupled device (CCD) of large number of pixels, other digital video camera capable of enhancing the picture quality of still picture and recording a moving picture is developed. In this case, when taking a moving picture, the digital video camera trims and puts out only part of pixels of the large number of pixels, and issues according to the number of pixels specified in the standard of digital VCR for consumer use (DV standard). In such prior arts, when taking a still picture, all pixels are used, and the picture quality of still picture is enhanced to a level equivalent to XGA (1024×768 pixels) or SXGA (1280×960 pixels). These prior arts are explained below.
FIG. 18 is a block diagram showing configuration of a conventional image sensing device, which is a single-CCD image sensing device. In the conventional image sensing device, using one CCD of multiple pixels, all pixels of the CCD 1 are used when taking a still picture, and some of the pixels necessary for the moving picture are cut out from the CCD 1 and used when taking a moving picture (trimming method). First, when taking a moving picture, the image sensing device discards signals corresponding to upper and lower ends of the screen taken by the CCD 1 by vertical high speed transfer, and utilizes only signals of vertical 480 pixels corresponding to the central area of the screen. Through an analog signal processing unit 2 and A/D converter 3, a matrix circuit 4 processes output signal of the CCD 1 sequentially, and, as a result, luminance signal (Y signal) and chrominance signal (C signal) are generated in the output of the matrix circuit 4. An electronic zoom circuit 5 discards signals corresponding to right and left ends of the screen of the output signals of the matrix circuit 4, zooms up by a proper magnification factor, and issues horizontal 720 pixels. Finally, the screen of the moving picture conforms to the DV standard of vertical 480 pixels and horizontal 720 pixels. When taking a still picture, the conventional image sensing device issues all pixels of the CCD 1, and if necessary, the electronic zoom circuit executes zoom process, converts into square pixels, and issues still picture image signals.
In the same configuration as in FIG. 18, the conventional image sensing device may also process to issue pixel signals corresponding to all pixels always from the CCD 1. In this case, in the moving picture, it is also possible to process to issue by shrinking in both horizontal and vertical directions (which is called shrink method).
Generally, the image sensing device of video camera is roughly classified into the single-CCD type and three-CCD type according to the unit number of the image sensing devices to use. In the single-CCD image sensing device uses one CCD device and it uses a color filter to obtain chrominance signals. The three-CCD image sensing device, by contrast, uses three CCD devices which generate R, G and B signals independently from each CCD. Therefore, it has such advantages as a high sensitivity, a high resolution, an excellent tone color, and further a wide dynamic range as compared with the single-CCD type. Moreover, the three-CCD image sensing device achieves an excellent high resolution, by shifting disposition of three CCDs in the two-dimensional position in the horizontal and vertical directions by ½ pixel each between the CCD for G and CCDs for R and B, that is, by the pixel shifting disposition method. However, so far, there is no effective method useful in both still picture and moving picture.
In the conventional image sensing device of such configuration, however, has the following problems.
First, in the trimming method, since only some of the pixels of the CCD 1 are used, the aspect of a picture in taking moving image is narrower than in taking still image.
In the shrink method, since all pixels of the CCD 1 are used also in taking moving picture, the aspect of a picture is not so narrower as compared with the case in taking still picture. However, in this case, the driving frequency of CCD in taking moving picture is high so as to increase its power consumption.
Further, in both methods, if the number of pixels of still picture is increased without changing the size of the optical system, the light receiving area per pixel is smaller, and the sensitivity of the CCD is lowered, and the picture quality deteriorates.
The invention is intended to solve these conventional problems, and it is hence an object thereof to realize an advantageous image sensing device not changed in the aspect of a picture between taking moving picture and taking still picture, capable of suppressing power consumption in taking moving image, and of no decrement of the sensitivity, by using the optical system of same size.